To achieve efficient chemical processing and manufacture, it is necessary to precisely control a number of processing parameters, such as temperature, pressure, mixing conditions, exposure of reactants to catalyst material, and exposure of reactants to actinic radiation, as well as conditions to achieve separation of the reaction products.
Conventional processing equipment suffers from a number of disadvantages. It has long been recognized in the chemical industry that "scale up" from laboratory bench scale to commercial production scale is difficult. Results achieved in the laboratory are often difficult to duplicate at production rates in production facilities. The conventional wisdom of "economy of scale" is based upon economic considerations which relate production rate (units of product per unit of time) to capital investment. This conventional approach results in less than optimum precision of control of chemical processing.
Conventional chemical processing equipment typically holds a relatively large volume of materials and consequently has a relatively large volume to surface area ratio. It is therefore likely that different portions of the reactant materials contained within such equipment are exposed to different histories of conditions. In the case of a conventional tank reactor, for example, even when temperature conditions at the walls of the reactor are well controlled, the portions of the reactants that are not in close proximity to the walls of the reactor may experience different temperature histories, especially if a significant temperature gradient exists, which might occur if the chemical reaction is strongly exothermic. Rapid stirring of the reactants may reduce this temperature history difference, but will not eliminate it. As a result of the nonhomogeneous temperature history, different portions of the reactants may chemically react differently. Undesired reactions may occur in portions of the reactants that are exposed to histories of higher than desired temperatures. This may result in the production of undesired waste products, which may be hazardous and which must be properly disposed of. In extreme situations reaction rates may accelerate to uncontrollable levels, which may cause safety hazards, such as potential explosions.
If, however, the volume to surface area ratio of the processing apparatus is substantially reduced, the degree of precision of control of homogeneity of temperature history of the reactants can be substantially improved.
It has been recognized that a high degree of flow turbulence enhances the ability to rapidly mix two or more reactants together. Rapid mixing is important for fast-acting chemical reactions. A high degree of turbulence is also known to enhance heat transfer. Thus, a structure having both a low volume to surface area ratio and a high degree of flow turbulence is particularly advantageous for precise control of chemical processing.
Individual units, such as miniaturized chemical reactors, have been fabricated from a stack of grooved metal plates, as in DE 3,926,466. It is also known to construct heat exchangers from a stack of grooved metal foils or plates or from grooved silicon wafers bonded to glass plates. Fabrication of small precise interior channels in structures, heretofore has been difficult. However, it has been achieved with diamond tipped metalworking machine tools primarily limited to straight channels, due to constraints imposed by the fabrication techniques. Such structures typically have a plurality of closely spaced straight parallel grooves with a manifold at each end of the grooves. Such straight-grooved structures, however, do not achieve the rates of mixing and the degree of turbulence in the mixture flow believed to be necessary for very fast chemical reactions.
Mixer assemblies having highly turbulent flow have been constructed by machining the desired passages and chambers in metal plates, using conventional metalworking techniques, and then assembling the plates into a stack and either clamping the stack together or permanently joining the stack, as by welding or soldering. An example is U.S. Pat. No. 3,701,619. Since conventional machine tool techniques are not well adapted to economically forming complex miniaturized structures, such structures cannot achieve particularly low volume to surface area ratios. Such devices are individual units and are not integral structures for chemical processing and manufacture.
The materials of construction of conventional chemical processing apparatus, such as steel and specialty iron alloys, furthermore may be subject to corrosion and wear, may have undesirable effects on catalytic activity, or may "poison" a catalyst. The apparatus of the present invention may be fabricated from a range of materials, selected to be compatible with the chemical process. Some of the specific techniques used to fabricate the apparatus are dependent on the material selected.
The present invention provides the capability to integrate one or more unit operations with sensors and control elements to meet the needs of a specific chemical reaction. A feature of the present invention is that it can be economically used in the laboratory, to make a range of precise sizes of a given element or operation unit, to perform the basic chemical reactions for determining optimum operating parameters for commercial volume production version of the integrated chemical processing unit. An additional feature of the present invention is that it can process multiphase materials. Advantages of the present invention include the elimination of many interconnections and joints, thereby reducing the potential for leaks. These and other objects, features and advantages will become better understood upon having reference to the following description of the invention.